This project concerns the effects that hormones, such as estrogen or prolactin, have on neurotransmitter receptors in the central nervous system. We have correlated biochemical changes in striatal dopamine receptors with behavioral changes in stereotypy or catalepsy. Both striatal DA receptor density and behavior of striatal origin are increased by prior estrogen treatment. Prolactin may be the mediator of these effects of estrogen or haloperidol. In addition, several toxins such as PBB have been tested for their estrogenic effects on the striatum. Ergot derivations which act opposite to estrogen in the pituitary have also been examined for their striatal effects. Since aging is associated with hormonal changes, aged rats are used in some studies in the assessment of the effects of hormones. These results may be relevant in neurologic, psychiatric, neuroendocrinologic disorders.